Method and apparatus for providing heated water for fracing

ABSTRACT

In an oil field fracing operation, a direct fire heater is provided that is mobile and self-contained on a trailer chassis. The direct fire heater has the maximum heat exchange possible between a burning gas and the fracing fluid by direct contact therewith. Recirculation is provided to maintain the fracing fluid at the desired temperature. A stack for the direct fire heater is removable for movement from one frac job or frac water heating site to another. Pellets in the stack helps insure a more complete heat exchange between the fracing fluid and the burning gas.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a method and apparatus for heating water for fracing oil and/or gas wells and, more particularly, to a portable direct fire heater that may be used in heating water for fracing.

2. Brief Description of the Prior Art

In the production of hydrocarbons, it is common to treat oil and/or gas wells with heated fluids such as water when hydraulically fracturing the formation. This hydraulic fracturing, known as a “frac” job, involves injecting large quantities of a heated fluid such as water into a subterranean formation under high pressure to hydraulically fracture the formation. Such a frac job is typically used to initiate production in low permeability reservoirs.

During fracturing, the fluid being injected into the well is under very high pressure which causes cracks in the underground formation where the fluid is being injected. The fluid being injected typically has a mixture of chemical additives. A typical example of such chemicals could be friction reducing polymers to improve flowability of the fluid being injected into the well under pressure. Also, a jell may be added to the fracing fluid so that when sand is added thereto, the jell will help carry the sand down into the well being fractured. The sand acts as a proppant so that after it is injected into the well and in the various fractures are under high pressure, once the pressure is released the sand is deposited into the fractures and remains therein to prop the fractures open after removal of the pressure. The propped open fractures will then allow the oil or gas to drain therefrom into the well for subsequent production. Frac jobs are typically performed on a newly drilled well, or after a couple of years of production when the flow in the well begins to decline.

Techniques for hydraulically fracturing subterranean formations by injecting a fracturing fluid down a well and into a formation under sufficient pressure to create fractures in the formation are well known. Commonly, the fracturing fluid is pumped through the tubing or casing in the well bore and into the formation to be fractured. The fracturing fluid is pumped at a sufficient rate and pressure to open a fracture in a preselected exposed formation that has been selected by perforating. The object is to extend the fracture from the well bore into the preselected area of the underground formation. Continued pumping of the fracturing fluid containing a propping agent (i.e., sand) into the fractures results in the proppant (i.e., sand) placement into the fractured zones. Following the pressurized treatment with a fracing fluid, fracing fluid is recovered from the well leaving the proppant remaining in the fracture, thereby preventing the closure of the fractures, which forms permeable channels from the well bore into the formation.

Frac jobs are typically performed at remote well sites and are usually completed in a short period of time. After fracing, the equipment used for fracing is removed. Consequently, the construction of a permanent heating facility to heat the fracing fluid is not cost effective. Instead, portable heat exchangers that can be transported to the remote well sites are commonly used. Because of the large volume of fracing fluid must be heated, a highly efficient energy source that transfers energy into heat for the fracing fluid is desired.

An oil fired frac water heater is shown in U.S. Patent Application Publication No. US 2010/0000508 A1 with a heat exchanger 50 through which the fracing fluid flows and is consequently heated. Therefore, the fire box 40 must heat the heat exchanger 50, which in turn will then heat the fracing fluid. Each time there is a conversion from one medium of energy to another form of energy, there are energy loses.

When a fracing fluid is heated and is waiting to be injected into the well, it will lose some of its heat. Therefore, it is important to continue to recirculate some of the fracing fluid for reheating. An example is shown in U.S. Patent Application Publication No. US 2010/0294494 A1, which uses a mixing manifold 20 for continuing to recirculate some of the fracing fluid and to maintain its temperature. Inefficiencies in the heater will simply be repeated upon reheating portions of the fracing fluid.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide an apparatus and method for providing heated fluid for fracing oil and/or gas wells.

It is a further object of the present invention to provide a direct fire heater for heating fracing fluid, which direct fire heater is portable and efficient.

A direct fire heater is provided where the flames and heat therefrom directly heat the fracing fluid (such as water) without the need for a heat exchanger. The direct fire heater can transfer anywhere from 10 million Btu's to 40 million Btu's directly to the fracing fluid. Thereafter, the direct fire heater can be mounted on a trailer and moved from one job site to another.

Further, the direct fire heater may be powered by alternative fuel sources such as liquid propane that would be hauled in, or gas from the wells within the field being drilled and/or produced. The type of fuel being used simply depends on the environmental conditions of the well site.

A source of fracing fluid such as cold water from a well, stream or a lake is fed to a portable trailer and filtered prior to being heated. The water is then fed into a direct fire heater for heating to an elevated temperature. From the direct fire heater, the fluid would flow to an appropriate storage facility such as frac tanks or a frac pit. From the storage facility, the heated water would go through a blender wherein the appropriate chemicals would be added along with the proponents (such as sand) prior to pumping into the well being fraced.

Prior direct fire heaters were not practical to use in remote well sites because they had a very high stack in which the heat from the flame would be transferred to the fluid. These high stacks were not portable because they could not be moved over commercial roadways to the site location. The present invention has a removable stack that can be laid flat inside the trailer containing the burner during transport. Upon getting to the new well site, the stack is then secured on the direct fire burner to give the maximum heat transfer between the flame and the fracing fluid. The fracing fluid may also be recirculated through the direct fire burner to continually maintain the fracing fluid at a predetermined temperature so the heated fracing fluid is continually available for use in the fracing operation. The pumps used in pumping the fracing fluid are self-priming pumps that can start automatically.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial view of the direct fire heater installed in a fracing system.

FIG. 2 is an alternative schematic view of the direct fire heater being used to heat water in a frac pit.

FIG. 3A is an alternative view of the direct fire heater heating water in a frac pit using a slip stream.

FIG. 3B is an alternative view of the direct fire heater heating water in a frac pit using a Y-valve.

FIG. 4 is an alternative view of the direct fire heater heating water that may be trucked to a fracing location.

FIG. 5 is an alternative view of the direct fire heater heating water that is accessible at numerous points for fracing.

FIG. 6 is a partial elevated sectional view of a direct fire heater in a portable trailer.

FIG. 7 is a partial sectional top view of a direct fire heater in a portable trailer.

FIG. 8 is an elevated partial sectional view illustrating burning within the direct fire heater to heat water.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning now to FIG. 1, a pictorial schematic of a fracing operation at the well head of a hydrocarbon-producing well is shown. A source of cold water comes in through cold water line 11. The source of cold water coming in through cold water line 11 may be from any convenient source such as a well, river or lake. The cold water line 11 has shut off with valve 13, which may be of any particular design such as a butterfly ball valve. The cold water flowing through the cold water line and shut off valve 13 flows through the X-connector 15 and valve 17 into direct fire heater 19 as will be explained in more detail. The direct fire heater 19 has a source of fuel such as propane tank 21. Propane tank 21 may be replaced by gas from the oil field being produced or some other suitable source.

Hot water from the direct fire heater 19 flows through hot water line 23 and hot water manifold 25 into frac tanks 27. Frac tanks 27 are simply storage units that are portable and may be moved to well sites.

To continue to maintain the water in the frac tanks 27 at a desired temperature, water flows from frac tanks 27 through return water manifold 29, frac tank return line 31, X-connector 15 and valve 17 back to the direct fire heater 19. In this manner, the direct fire heater 19 can continue to maintain water in frac tanks 27 at a desired temperature. A blending valve 33 is connected through T-connection 35 to the hot water line 23. The blending valve 33 and/or shut off valve 13 allows for some of the hot water from the direct fire heater 19 to be recirculated through X-connector 15, valve 17 and back to direct fire heater 19. In this manner, the operator can control the temperature of the water being heated. The regulation of recirculated water is aided by a return water valve 37 that can control the amount of return water flowing through the frac tank return line 31.

Normally, the optimum temperature of the water for fracing is between 70° and 80°. Therefore allowing for some cooling, the water in frac tanks 27 should be maintained above 80°. In cold climates, the water in frac tanks 27 should be slightly warmer than water in temperate climates.

From the frac tank 27 water flows through hot water manifold 25 and a warm water feed line 39 to a blender 41. Inside the blender 41 various materials are added to the warm water such as (a) chemicals and/or (b) proppants, such as sand. A frac sander 43 feeds sand through sand feed 45 into blender 41. Sand feed 45 may be of any conventional means such as a pressurized airline, a conveyor type feeder, or an auger type feeder. The chemicals being added to the warm water feed line 39 inside of blender 41 will vary according to the formation. Jells for example may be included to maintain the sand in a suspended condition. The sand will become the propping agent once the pressure is released to maintain the fractures in the open condition to get maximum production from the formation. Other chemicals or biocides may be added in blender 41 as is needed.

From the blender 41, the mixture will flow through the blended warm water line 47 to the pumping vehicle 49. The pumping vehicle 49 will pressurize the blended mixture to a very high pressure, which high pressure blended mixture will flow through high pressure line 51 to the well head 53 and into well 55 being fraced. Pressure of the blended mixture is very high, normally exceeding 1,000 psi. The objective is for the blended mixture to be forced into fractures in the underground formation that contains the hydrocarbons. Later, when the pressure is released, some of the sand will remain in the fractures to keep the fractures open, thereby allowing oil or gas production through the fractures.

On some frac jobs, frac water may not be heated at the frac site. Instead, water may be heated at a frac pit 57, as shown in FIG. 2, and delivered to the frac tanks at the frac site via a water pipeline. Direct fire heater 19 may have a hot water line 23 flowing to the frac pit 57. A cold water intake line 59 delivers water from the frac pit 57 to the direct fire heater 19 for heating before flowing through the hot water line 23 back into the frac pit 57. As the circulation of water occurs between the frac pit 57 and the direct fire heater 19, the water inside of the frac pit 57 will be warmed. Warm water from the frac pit 57 is delivered through frac water pipeline 61 to the frac tanks at the frac site (not shown) for injection into the well being fraced.

The direct fire heater 19 has a heater stack 63 to get the maximum heat transfer from the flames of a direct fire heater 19 to water used for fracing. The flames in the direct fire heater 19 may be fueled by either natural gas pipeline 65, which can be from the field being produced, or from propane tank 21. Because the propane being delivered in the propane tank 21 will probably be in liquid form, vaporizers 67 and 69 may be used to convert the liquid propane to gas prior to injection into the direct fire heater 19. The dual vaporizers 67 and 69 provide additional capacity and backup. The direct fire heater 19 will either use natural gas through natural gas pipeline 65 or propane from propane tank 21. These are alternative fuel sources for the direct fire heater 19. Also, to operate various electrical controls within the direct fire heater 19, a generator 71 will generate the electricity needed. Generator 71 may be driven by any convenient source such as propane from propane tank 21 or natural gas from natural gas pipeline 65.

There are numerous different configurations in which the direct fire heater 19 can be used to heat the fracing fluid. For example, in FIG. 3A, the direct fire heater 19 draws cold water from the frac pit 57 through cold water intake line 59. After the cold water is heated in the direct fire heater 19 with the stack 23, hot water output flows through hot water output line 73, which is blended with cold water from the frac pit 57 to deliver warm water to the frac site through warm water line 75. This method is referred to as a slip stream method with hot water and cold water being blended to give warm water. A pump 77 pumps the cold water from the frac pit 57, which is combined with the hot water from the hot water output line 73 in a slip stream fashion to deliver warm water through the warm water line 75 to the frac site.

Referring to FIG. 3B, which is a variation of the slip stream method shown in FIG. 3A, cold water is taken from the frac pit 57 through cold water intake line 79 for delivery to the direct fire heater 19. After the water is heated in the direct fire heater 19 and stack 63, the hot water is delivered through hot water line 81 and Y-valve 83 so that a portion of the hot water from hot water line 81 will flow back to the frac pit 57 through warm water return line 85 and a portion of the warm water will flow through the warm water frac line 87 to the frac site (not shown). The hot water contained in the hot water line 81 may be blended with cold water received via cold water line 89, which cold water is pumped by cold water pump 91. The cold water in cold water line 89 and the hot water in hot water line 81 are blended together to give warm water of the desired temperature.

Referring to FIG. 4, another option for the direct fire heater 19 to heat fracing fluid is shown. Cold water is fed to the direct fire heater 19 through cold water intake line 93. The cold water will be heated in the direct fire heater 19 and the heater stack 63 prior to delivery through hot water line 95 to large water tanks 97 and 99. The large water tanks 97 and 99 will simply hold the water until tanker trucks come by on drive thru 101 to the truck water filling stations 103 and 105. The tanker trunks will be filled at either truck water filling station 103 or 105. Thereafter, the warm water is taken to the frac site. It is anticipated that the distance between the truck water filling stations 103 or 105 and the frac site will not be that great (less than 40 miles). For example, this system could be used in a unitary oil or gas field being fraced. Water Depot configuration may vary based on the space available and other considerations. An example of another configuration is similar to that of a gas filling station whereby there are multiple lanes that straddle the heater and tanks.

An alternative method of heating frac fluid is shown in FIG. 5. The fluid to be heated may be drawn from any particular water source 107 such as a lake. The cold water feeds through cold water pipeline 109 from the water source 107 to the super direct fire heater 111. The super direct fire heater 111 operates similar to the direct fire heater 19, except the super direct fire heater 111 has multiple heater stacks 113. Each of the heater stacks 113 will have a separate burner (as will be subsequently described) for heating the cold water received through cold water pipeline 109. The super direct fire heater 111 is located at the frac work yard 115 or a centralized water pipeline riser point, which is in the vicinity of the various wells being fraced. Hot water from the super direct fire heater 111 is delivered to hot water pipeline 117. Hot water from hot water pipeline 117 may feed to a number of different risers, such as risers 119A through 119G. Each of the risers 119A through 119G will have a valve that can be opened and hot water received there through.

The direct fire heater 19, as previously described in conjunction with FIGS. 1-4, has one heater stack 63 and may generate approximately 16 million Btu's per direct fire heater 19. However, the super direct fire heater 111 has multiple heater stacks 113 and may generate approximately 45 million Btu's per super direct fire heater 111. Regardless of the type of direct fire heater being used, the water is never heated over its boiling point to change the water into a vapor.

Referring now to FIGS. 6 and 7 in combination, the direct fire heater 19 will be explained in more detail. The direct fire heater 19 is contained within a trailer chassis 121 having a floor 123 with enclosed side walls 125 and top 127. The cold water to be heated for fracing comes in through cold water inlet 131. Motor 133 drives pump 135 which sucks the cold water in through cold water inlet 131. Pump 135 is a self-priming, progressive cavity pump that can pull a vacuum to suck water from approximately 20 ft. there below. Output of the pump 135 flows through discharge line 137 to a bank of filters 139. The filters 139 will remove large solid particles from water. Since the water may be drawn from lakes or streams, large solid particles may be sucked up with the water. The bank of filters 139 will remove the large solid particles. Filter water line 141 feeds the filtered water to the heater stack 63. At the heater stack 163, the filtered water will flow through a valve 143 and spray line 145 to a spray nozzle 147. At the bottom of the heater stack 63 is the main heater chamber 149. At the bottom of the main heater chamber 149 setting on floor 123 is a pump 151 driven by pump motor 153. Pump 151 draws heated water from the bottom of the main heater chamber 149 into hot water intake line 155. The pump 151 will pump hot water through hot water line 159 and out hot water discharge valve 161, which hot water can then be used in a fracing operation (see FIG. 6).

Fuel from either a propane tank 21 or natural gas pipeline 65 (see FIG. 2) feeds through natural gas inlet line 163 to a natural gas regulator 165 (see FIG. 7) or propane inlet line to a propane regulator. The regulated natural gas or propane will feed through regulated gas line 167 to burners 169. While the direct fire heater 19 shown in FIG. 7 has two burners 169, it could be built with a single burner. The burners 169, which are shown in FIG. 7 (but not FIG. 6) inject a burning flame through burner port 171 into main heater chamber 149.

For the gas inside of the burners 169 to completely burn, it must have a source of air. Air blower 173 sucks air in through louvers 158 for induction through the air duct 175 into burners 169 as can be seen in FIG. 7. Because a massive amount of fuel is being burned in burners 169, air blower 173 has to force a large quantity of air into the burners 169 for a complete combustion of the fuel. This operates on the same principle as a supercharger or turbo charger. The fuel and air delivery system as shown in FIG. 7 has been eliminated from FIG. 6 for the purpose of clarity. However, the burners 169 (not shown in FIG. 6) fit inside of burner port 171.

At the front of the trailer chassis 121 is located a generator 177 for generating any electricity needed to operate the direct fire heater 19. When moving to or from a frac site, the heater stack 63 may be removed and laid down inside of stack container 179 at the front of the trailer chassis 121. The stack 63 will be adjacent to the generator 177.

Referring now to FIG. 8, a simplified cross-sectional view of the direct fire heater 19 is shown. All of the connections for the water have been removed leaving only the fuel connections. In the heater stack 63 above the main heater chamber 149 is located heat exchanger pellets 181, which heat exchanger pellets 181 rest on perforated plate 183 located near the bottom of the heater stack 63. A spray nozzle 147 (previously shown in FIG. 6) is used to spray water 185 (or other suitable fracing fluid) onto the heat exchanger pellets 181. The water 185 flows through the heat exchanger pellets 181, through perforations in perforated plate 183 and into the main heater chamber 149.

On the side of the main heater exchanger 149 is located burner 169. Burner 169 receives propane or natural gas through fuel delivery line 187. The amount fuel flowing through fuel delivery line 187 is controlled by fuel supply solenoid 189 which operates control valve 191. Gas regulator 165 regulates the pressure of the fuel being delivered to burner 169. While not shown in FIG. 8, air from the air blower 173 also feeds into the burner 169 (see FIG. 7). As the air and fuel are discharged from the burner 169 into burner port 171, they are ignited into flames 193, which flames flow into main heater chamber 149. The flames 193 provide direct fire heat to the water 185 as well as heating the heat exchanger pellets 181. The heated air will rise and blow out air ducts 195 at the top of stack 63. The flames 193 are ignited in an area that is referred to as the combustion chamber 197.

From the bottom of main heater chamber 149 motor 153 operates pump 151 to pump heated water through check valve 199 (see FIG. 6) for delivery to the hot water line 159. Sensor 201 monitors the temperature of the water in water line 159 to determine if more or less fuel needs to be added to the burner 169 via fuel supply solenoid 189 and control valve 191.

Also as indicated by the arrows, air will circulate around inner chamber 203 to absorb the heat, which heat will then be transmitted either to the water 185 or the heat exchange pellets 181. Likewise, an inner combustion chamber 198 has a space there around where air can flow prior to discharge into main heater chamber 149 prior to flowing upward through water 185 and heat exchanger pellets 181 which will receive the heat therefrom.

Referring back to FIG. 6, a recirculation feature is provided by recirculation line 207 which allows hot water from hot water line 159 to be recirculated through recirculation valve 209 to filter water line 141. In this manner, if it is desired to recirculate water within the direct fire heater 19, it can be recirculated. 

What I claim is:
 1. An apparatus for supplying heated water to a well to be fraced comprising: a source of water; a direct fire heater for heating some of said water from said source; a source of gas for burning in a combustion chamber of said direct fire heater; storage facility for temporarily storing said heated water; a source of a proppant such as sand; a blender for blending together said heated water, said proppant and chemicals into a fracing mixture; a pump for pumping said fracing mixture under high pressure into said well to be fraced; said burning gas in said direct fire heater transferring heat therefrom to said water being sprayed from a top down through a heater stack into a main heater chamber, which main heater chamber receives said burning gas from said combustion chamber mounted on a side of said main heater chamber.
 2. The apparatus for supplying heated water to the well to be fraced as recited in claim 1 wherein said heater stack is removable from said main heater chamber of said direct fire heater so that said direct fire heater is transportable in a trailer chassis.
 3. The apparatus for supplying heated water to the well to be fraced as recited in claim 2 wherein water pumps pump said water through a spray nozzle mounted in said top of said heater stack and subsequently into said storage facility.
 4. The apparatus for supplying heated water to the well to be fraced as recited in claim 3 wherein some of said heated water is recirculated to maintain said heated water in said storage facility at a predetermined temperature.
 5. The apparatus for supplying heated water to the well to be fraced as recited in claim 4 wherein said direct fire heater is portable from one frac site to another frac site.
 6. The apparatus for supplying heated water to the well to be fraced as recited in claim 5 wherein said heater stack has a perforated plate near the bottom thereof, heat exchange pellets being held above said perforated plate in said heater stack, said heat exchange pallets being heated by said burning gas and transferring said heat to said water being sprayed thereon.
 7. The apparatus for supplying heated water to the well to be fraced as recited in claim 6 further comprising filters between said source of said water and said spray nozzle to remove solids from said water.
 8. The apparatus for supplying heated water to the well to be fraced as recited in claim 7 wherein said direct fire heater has a generator for generating electricity to run said direct fire heater, said generator being mounted on said trailer chassis.
 9. A method of heating fracing fluid for a hydrocarbon well to be fraced comprising the steps of: receiving water from a source into a direct fire heater; igniting a source of fuel in a combination chamber of said direct fire heater; blowing air into said combustion chamber of said direct fire heater to aid combustion of said fuel; discharging burning fuel and air from said combustion chamber into a main heater chamber with heated air and flames flowing upward through a heater stack above said main heater chamber; spraying said water from a top of said heater stack, through said heater stack and into said main heater chamber; collecting heated water in a bottom of said main heater chamber; and pumping heated water from the bottom of said main heater chamber to a warm water collecting container prior to injection into said well.
 10. The method of heating fracing fluid for a hydrocarbon well to be fraced as recited in claim 9 includes an additional step of recirculating some water from said warm water collecting container to maintain water therein at a predetermined temperature.
 11. The method of heating fracing fluid for a hydrocarbon well to be fraced as recited in claim 10 includes a further step of heat exchanging between heat exchanger pellets in said heater stack and said water sprayed there over.
 12. The method of heating fracing fluid for a hydrocarbon well to be fraced as recited in claim 11 includes the use of multiple combustion chambers for each main heater chamber.
 13. The method of heating fracing fluid for a hydrocarbon well to be fraced as recited in claim 12 includes the use of multiple heater stacks.
 14. The method of heating fracing fluid for a hydrocarbon well to be fraced as recited in claim 9 wherein said heater stack is removable.
 15. The method of heating fracing fluid for a hydrocarbon well to be fraced as recited in claim 14 wherein said direct fire heater is mounted on a trailer and is transportable over public roads. 